Method and system of preheating

ABSTRACT

A method and system of heating combustion air before the combustion air is received by a hot water or steam boiler. A solar panel oriented to receive radiant energy from the sun is used to heat a fluid. A circulating pump moves the hot fluid through a closed loop to a preheat exchanger that is located in the combustion air stream of the hot water or steam boiler. When the combustion air blower of the hot water or steam boiler is on, heat from the heated circulating fluid in the preheat exchanger is transferred to combustion air going through the preheat exchanger to the combustion air blower of the boiler and to the boiler.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and system of using solar energy to heat a fluid in solar panels and using the heated fluid in conjunction, and as a first step, with any other known method to preheat combustion air.

2. Background of the Invention

In these days of rising fuel costs due to inflation and scarcity of fuel supplies, it is desirable to provide a more efficient heating system which can maximize the quantity of heat delivered by a boiler for each unit of fuel consumed. Currently, many steam and hot water heating systems are inefficient which results in increased fuel usage and the increase cost associated with using additional fuel.

Various methods have been proposed in an attempt to reduce the cost of operating heating systems by extracting greater amounts of heat energy from the fuel used.

For example, U.S. Pat. No. 7,007,742 discloses using heat retrieved from flue gas passing through a stack to improve the efficiency of a boiler by increasing the supply of domestic hot water.

U.S. Pat. No. 5,607,011 discloses using an evaporative fluid circulating in a closed heat exchanging circuit to transfer heat energy from a relatively hot flue gas stream to a relatively cold combustion air stream. The fluid is heated and evaporated and then conducted to a condenser heat exchanger to give up the recovered heat energy to a combustion air stream. While the combustion air stream is being heated, the vapor of the working evaporated fluid is cooled and condensed, and then returned back to an evaporator heat exchanger.

U.S. Pat. No. 5,308,187 discloses placing a plurality of parallel pipes beneath the surface of a parking field. As the surface of the parking field is heated by the sun, the air in the pipes is heated. This heated air is used as precombution air in an oil, coal or gas burner.

U.S. Pat. No. 4,899,728 discloses preheating ventilation air for a building by providing a solar-energy absorbent collector panel with a plurality of air-inlet openings which communicate with air on a south-facing wall. Outside air passing upwardly along collection channels behind the panel is heated by the heat of the panel. The outside air, passing up along the panel is withdrawn into an air collection channel and expelled into the interior of the building.

U.S. Pat. No. 4,739,826 discloses apparatus for using hot flue gas to preheat air for combustion where the surfaces of the heat exchange elements which are exposed to the flue gas are provided with a coating which acts as a catalyst for NO.sub.x reduction of the flue gas.

U.S. Pat. No. 4,617,109 discloses using portions of low pressure steam and superheated medium pressure steam for preheating combustion air for a tubular steam cracking furnace.

U.S. Pat. No. 4,189,922 discloses converting solar energy into electric power by heating preheated and precompressed air in a solar heater before being sent to a turbine connected to an electric power generator.

U.S. Pat. No. 4,126,121 discloses a plurality of thermoplastic sheets of film arranged to form complementary first and second heat transfer chambers for a pressurized fluid that is supplied to one of the chambers and then flows to the other of the chambers through an opening in the film intermediate which is between where the fluid is heated when the film is exposed to sunlight.

What is needed is a new method and system of preheating combustion air using solar energy to reduce the costs of operating boilers.

SUMMARY OF THE INVENTION

In an embodiment, there is disclosed a method and system for heating combustion air before the combustion air is received by a burner of a hot water or steam boiler where a solar panel is oriented to receive radiant energy from the sun for heating a fluid. A circulating pump is provided to move the heated fluid from the solar panel through a closed loop that includes a preheat coil. Combustion air going to a combustion air blower passes through the preheat coil where heat from the heated fluid is transferred to the combustion air.

The foregoing has outlined, rather broadly, the preferred feature of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention and that such other structures do not depart from the spirit and scope of the invention in its broadest form.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, features, and advantages of the present invention will become more fully apparent from the following detailed description, the appended claim, and the accompanying drawings in which similar elements are given similar reference numerals.

FIG. 1 is a schematic diagram showing a system of preheating the boiler combustion air with the sun energy in accordance with the principles of the invention; and

FIG. 2 is a partial perspective view of a solar panel with dampers over the solar panel.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to preheating combustion air for hot water or steam boilers with renewable energy from the sun.

Referring to FIG. 1, there is shown a schematic diagram of a system 10 that uses solar panels to heat a fluid used to preheating boiler combustion air with radiant energy from the sun. A solar collector 12 is a device that converts radiant energy from the sun into heat and uses the obtained heat to heat a fluid.

A solar hot water panel used to generate hot water is usually a weatherproofed, insulated box containing a black metal absorber sheet with built in pipes placed in the path of sunlight where solar energy heats up water in the pipes.

Generally solar panels consist of a flat-plate absorber, which intercepts and absorbs the solar energy; a transparent cover that allows solar energy to pass through but reduces heat loss from the absorber; a fluid such as antifreeze and water flowing through tubes in the solar panel to remove heat from the absorber; and a heat insulating backing.

Where freezing is a possibility, solar panels that can freeze without damage have been developed. Their fluid channels are typically made of food grade polymers such as silicone rubber, which is flexible and remains stable, and the fluid can be a mixture of ethylene glycol and water.

When the fluid in the solar panel is a mixture of water and propylene glycol, the temperature that the fluid will freeze depends on the proportion of propylene glycol in the mixture. The use of glycol lowers the water's heat carrying capacity only marginally.

In a preferred embodiment of the invention, the solar panels 12 use a mixture of propylene glycol and water, hereinafter referred to as glycol/water, as the fluid in the solar panels. Radiant energy from the sun that is collected by solar panels 12 is transferred to a glycol/water fluid that is circulated in a closed loop 14 by pump 16 to a preheat coil 18.

A photo cell 20 is positioned to detect the presence or absence of sun light on the solar panels and is coupled to turn off the pump when the solar panels are not receiving sun light to save energy. As the temperature of the glycol/water mixture increases, so does its volume. An expansion tank 22 that is connected to a closed loop 14 is provided to receive any increase in the volume of the glycol/water that is due to an increase in temperature.

A circulating pump 16 moves the heated glycol/water solution around a closed loop which includes the solar panels 12, a fluid-to-air heat exchanger 18 (preheat coil) where heat from the solution is used to heat combustion air before it reaches the hot water or steam boiler combustion blower. The temperature of the circulating glycol/water solution is monitored by a sensor 26 that is connected to the closed loop 14 to monitor the temperature of the glycol/water mixture. Electrically operated motors 27 are connected to close dampers 30 positioned over solar panels 12 when the temperature of the glycol/water solution gets too hot.

A motorized damper (Combustion air Damper) 40 or variable frequency drive control the flow of combustion air through the combustion air blower 32 of the hot water or steam boiler. One damper 40 is located upstream of the preheat coil 18 and the combustion air blower 32, and the other damper 38, a motorized freeze damper, is located down stream of the preheat coil 18.

Combustion air blower 32 moves combustion air from either indoor air intake 34 or out door air intake 36, or from each through the motorized freeze protection damper 38, the preheat coil 18, and a combustion air damper 40 to a boiler 42. The combustion air damper 40 controls the amount of combustion air that is moved by the combustion air blower 32 that is required by the burner of the boiler 42.

During operation, when the boiler is off, the combustion air blower will be off and combustion air will not be moving. At this time the pump 16 will also be off and the dampers over the solar panels will be closed. If the combustion air damper 40 is replaced with a variable frequency drive, the freeze protection damper 38 will be closed to prevent cold air from moving from the outside through the preheat coil 18, and the combustion air blower 32 to the boiler 42 where the cold air may freeze the water in the boiler.

Referring to FIG. 1, there is shown a system 10 for recovering heat from solar panels 12 to preheat boiler combustion air. Heat from the solar panels is transferred to a Glycol/water solution which moves past a temperature sensor 26 to a preheat coil 18. When the temperature sensor 26 detects that the glycol/water solution is approaching its boiling point, it will activate motors 27 to close the dampers 30 which prevents sun light from entering the solar panels. The glycol/water solution is circulated through solar panels and the preheat coil 18 by circulator pump 16. In preheat coil 18, heat from the glycol/water solution is transferred to combustion air that is being moved to the boiler 42 by combustion air blower 32. Combustion air damper 40 which is located up stream of the combustion air blower 32 controls the flow of air through the preheat coil 18 to modulate the flow of heated combustion air fed to burner. Thus, as the flow of heated air to the boiler is restricted, so is the flow of air through the preheat coil restricted. This change in the volume of air flowing through the preheat coil will cause a change in the temperature of the glycol/water solution. As the air flowing through the preheat coil decreases, the temperature of the glycol/water solution increases. The combustion air that flows thru freeze protection damper 38 can be from an indoor air intake 34, and outdoor air intake 36, or from both.

During operation, when the hot water or steam boiler 42 is on and the system is energized, the hot water or steam boiler 42 is operating, the combination air blower 32 is on, circulation pump 16 is on, and the outside air freeze protection motorized damper 38 is open to pass combustion air to preheat coil 18. If, when the system is on, the temperature of the ethylene glycol/water solution rises to be within 20 degrees F. of its boiling point, temperature sensor 26 will operate and close the dampers 30 that cover the solar panels to prevent sun light from reaching the solar panels. The temperature at which the ethylene glycol/water solution will boil is determined by the percentage of ethylene glycol that is in the solution because the higher the percentages of ethylene glycol the higher the boiling point. In operation, the actual temperature at which the temperature sensor 26 operates to close the dampers 30 over the solar panels is set by the operator.

Referring to FIG. 2, there is shown a roof mounted solar panel 12 located under dampers 30 and connected to an insulated closed loop 14.

When the boiler is off, the circulating pump 16 will be off, the combustion air blower 32 will be off, and the freeze protection motorized damper 38 will be closed.

Controls for operating the various components are integrated with boiler controls and/or the building automation system.

In the invention disclosed, heat from the solar panels is used to preheat the boiler combustion air to improve the operating efficiency of the hot water or steam boiler. Solar energy heat from solar panels is used to heat a circulating solution of ethylene glycol and water. The heated glycol/water solution circulates through a preheat coil 18 where combustion air that is being fed to a hot water or steam boiled is heated. The preheat coil is a fluid to air heat exchanger. The temperature sensor used to monitor the temperature of the glycol/water solution is coupled to control the motorized dampers over the solar panels. The combustion air motorized damper (Which can be replaced by a variable frequency drive) is used to control the flow of unheated air to the preheat coil and to the combustion chamber of the hot water or steam boiler.

It is to be understood that the sizes of the equipment here disclosed and the temperature settings that are used will depend upon the specific equipment used and its application.

The present invention materially contributes to increasing the utilization of energy from the boilers by preheating the combustion air with radiant energy from the sun, saving fuel.

Based upon the foregoing, it will be apparent that there has been provided a new and useful method and system to use Solar Energy to preheat the boiler combustion air, which will save energy.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to the preferred embodiments, it will be understood that various omissions and substitutions and changes of the form and details of the apparatus illustrated and in the operation may be done by those skilled in the art, without departing from the spirit of the invention. 

1. A system for heating combustion air before the combustion air is received by a combustion air boiler of a hot water or steam boiler comprising: a solar panel oriented to receive radiant energy from the sun for heating a fluid; a circulating pump for moving heated fluid from said solar panel through a closed loop; and a preheat exchanger coupled to said closed loop to receive said heated circulating fluid to transfer heat from the circulating fluid to combustion air going to a combustion air blower, a combustion air damper and a boiler.
 2. The system of claim 1 wherein said preheat exchanger is a fluid-to-air heat exchanger.
 3. The system of claim 2 wherein said preheat exchanger is located downstream of said combustion air blower.
 4. The system of claim 1 wherein said combustion air damper controls the amount of combustion air that is delivered to the boiler.
 5. The system of claim 2 further comprising: a first damper coupled to said solar panel to selectively block sunlight from said solar panel.
 6. The system of claim 2 further comprising: a second damper located upstream of the preheat exchanger to control the amount of cold air that flows through the preheat exchanger.
 7. The system of claim 5 further comprising: a temperature sensor coupled to close the first damper when the heated fluid from said solar panel reaches a preset temperature.
 8. The system of claim 7 further comprising: a photo cell coupled to turn off power to the pump when said solar panel is nor receiving sunlight.
 9. The system of claim 8 further comprising: an expansion tank coupled to the closed loop.
 10. The system of claim 9 further comprising: a combustion air motorized damper for controlling the amount of air that passes through the preheat exchanger.
 11. The method of heating combustion air before the combustion air is received by a combustion air blower of a hot water or steam boiler comprising: orienting a solar panel to receive radiant energy from the sun for heating a fluid; providing a circulating pump for moving heated fluid from said solar panel through a closed loop; and coupling a preheat exchanger to said closed loop to receive said heated circulating fluid to transfer heat from the circulating fluid to combustion air going to a combustion air blower, a combustion air damper, and a boiler.
 12. The method of claim 11 wherein said preheat exchanger is a fluid-to-air heat exchanger.
 13. The method of claim 12 wherein said preheat exchanger is located downstream of said combustion air blower.
 14. The method of claim 11 wherein said combustion air damper controls the amount of combustion air that is delivered to the boiler.
 15. The method of claim 12 further comprising: coupling a first damper to said solar panel to selectively block sunlight from said solar panel.
 16. The method of claim 12 further comprising: providing a second damper upstream of the preheat exchanger to control the amount of cold air that flows through the preheat exchanger.
 17. The method of claim 15 further comprising: providing a temperature sensor to close the first damper when the heated fluid from said solar panel reaches a preset temperature.
 18. The method of claim 17 further comprising: providing a photo cell to turn off power to the pump when said solar pane is nor receiving sunlight.
 19. The method of claim 18 further comprising: connecting an expansion tank to the closed loop.
 20. The method of claim 19 further comprising: providing a combustion air motorized damper for controlling the amount of air that passes through the preheat exchanger. 